X-BIONIC Energizer works to maintain body temperature at an optimum 37 degrees, cooling you down when you sweat, and keeping you warm when you're cold.Its clever regulation system works with the most reliable of starters: your sweat. One-of-a-kind, and effective with its cooling power starting exactly when you need it.If no sweat is present, then a unique process uses air heated by the body as thermal insulation.The award-winning X-BIONIC Energizer has been developed by scientists and tested by endurance athletes.